1. Field of the Invention
The present invention pertains to filters used in electronic communication devices, and particularly to comb-line filters applicable to wireless communication devices and systems.
2. Prior Art
Generally, wireless communication devices such as mobile phones or notebook computers with mini-PCI/PCMCIA/USB wireless cards are designed to be as small as practicable, so that users can conveniently take the wireless communication devices anywhere they want to go. Since wireless filters are necessary components of wireless communication devices, one solution to reduce the size of a wireless communication device is to reduce the size of the wireless filter used therein.
In one such solution, China Patent Publication No. 1,317,847, published on Oct. 17, 2001, discloses a comb-line wireless filter. FIG. 3 herein is a schematic representation of a structure of that comb-line wireless filter. The comb-line wireless filter comprises a filtering top layer 100, and a grounded bottom layer 120 for supporting the filtering top layer 100. A pair of micro-strip lines 108a, 108b are fixed on the filtering top layer 100 in a parallel and linear manner. The pairs of micro-strip lines 108a, 108b are connected to the grounded bottom layer 120 by way of two holes 104a, 104b, and coupled with two capacitance compensators 110a, 110b through two holes 102a, 102b. The micro-strip line 108a is connected to an input end 106a, and the micro-strip line 108b is connected to an output end 106b. It is possible to add some parallel micro-strip lines between the micro-strip line 108a and the micro-strip line 108b. If this is done, relevant holes and capacitance compensators should be added.
The above-described micro-strip lines 108a, 108b are designed in the parallel and linear manner. When the comb-line wireless filter needs the micro-strip lines 108a, 108b to be of a given minimum length, it is problematic to minimize the overall size of the comb-line wireless filter. Consequently, what is needed is a comb-line wireless filter having transmission lines (strip lines or micro-strip lines) with a configuration that can reduce the overall size of the comb-line wireless filter.